● ResearchWe make a study of an ecologically friendly new material, which is rich-abundant and is made from non-toxic elements, for an electric device. For example, they are diamond which is a high-pressure and high-temperature phase, diamond-like carbon which is a non-equilibrium phase, beta iron disilicide which is a candidate semiconductor for an opt-electric device and the others. We fabricate them by the film preparation method using a laser and a plasma technology. In addition, we develop the film preparation system in cooperation with some small and medium enterprises. The detail subjects of the study are as follows.【Low temperature growth of diamond films by pulsed laser deposition】【Fabrication of hydrogen-free diamond-like carbon films by physical vapor depositions and their application for coating】【Research concerning ecologically friendly semiconductors and their application for electric devices】【Research in a semiconductor / ferromagnetic metal superlattice】【Research in a new cathode material for a lithium ion battery】【Development of the innovative film preparation system】

● EducationI belong to Department of Engineering Sciences for Electronics and Materials. My additional affiliation for graduate school education is Department of Applied Science for Electronics and Materials. Besides, I contribute to the undergraduate school education and have the following classes: “Lecture on mechanics and practice”, “Elemental experiment on physics” and “Soft energy for sustainability”.

● Social activitiesI contribute to the study group of The Japan Society of Applied Physics as a manager and contribute to Kyushu Chapter of The Japan Society of Applied Physics as an administrator.In Kyushu University, I hold a additional post as a technical advisor of Kyushu TLO Company, Limited. In the year 2003, I had lectures in an open class and a seminar of the graduate school.I have a lecture of the training institute organized by The Japan Cooperation agency (JICA) and Kyushu University.

Research

Research Interests

Fabrication of new spintronics devises based on ferromagnetic Fe3Si/semiconducting FeSi2 heterostructural artificial lattices using nanofabrication techniqueskeyword : Fe-Si, spintronics, CPP, lithography2011.04【Research in a semiconductor / ferromagnetic metal superlattice】
There have been few studies for the hetero-structure, such as the ferromagnetic metal /semiconductor multi-layered film, because the fabrication is extremely difficult. However, this hetero-structure has a possibility that the anti-ferromagnetic and ferromagnetic coupling among the ferromagnetic layers can be switched through the intermediary of the semiconducting layers, whose electrical band structure can be changed by the heat and photons. Fe-Si system has both the semiconducting phases such as beta-FeSi2, amorphous FeSi2 and FeSi, and the ferromagnetic ones such as Fe3Si and Fe、and expected as a new candidate for spintronic. We fabricate the Fe3Si or Fe / nanocrystalline (NC) FeSi2 multi-layered films, and study a new physical properties at optical, electrical and magnetic points of view..

Applications of ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCDa/-C:H) films to phtodiodes including solar cellskeyword : ultrananocrystalline diamond, UNCD, photodiodes, photoviltaics, solar cells2011.04【Low temperature growth of diamond and nanocrystalline diamond films by pulsed laser deposition】Diamond has many excellent properties such as the highest hardness, high chemical inertness, low friction coefficient and high optical transparency and thus it is expected for a variety of applications. In addition, it overcomes ecological and resources problems. Nanocrystalline diamond is also expected as a candidate for coating and heat sink, because it is easy to be grown and it has a smooth surface like DLC, and because it is stable for temperature and has high heat conductivity similarly to diamond. In this study, we attempt to grow them at a low substrate temperature by pulsed laser deposition in order to realize the application for a heat sink coating and an electric device..

Farbrication of ultrananocrystalline diamond films by pulsed laser depositionkeyword : ultrananocrystalline diamond, UNCD. pulsed laser deposition, PLD2000.04～2006.03【Low temperature growth of diamond and nanocrystalline diamond films by pulsed laser deposition】Diamond has many excellent properties such as the highest hardness, high chemical inertness, low friction coefficient and high optical transparency and thus it is expected for a variety of applications. In addition, it overcomes ecological and resources problems. Nanocrystalline diamond is also expected as a candidate for coating and heat sink, because it is easy to be grown and it has a smooth surface like DLC, and because it is stable for temperature and has high heat conductivity similarly to diamond. In this study, we attempt to grow them at a low substrate temperature by pulsed laser deposition in order to realize the application for a heat sink coating and an electric device..

Applications of iron disilicides to photovoltaics and NIR sensorskeyword : beta iron disilicide, nanocrystalline iron disilicide, sputterng 1999.04【Research concerning ecologically friendly semiconductors and their application for electric devices】
Nowadays, it is necessary for the materials tractable for the industrial application to have not only excellent material properties but also favorable ecological properties such as non-toxicity, abundance, and recyclability. Semiconducting beta-FeSi2 has excellent properties such as a direct optical band gap of 0.8-0.85 eV, a large optical absorption coefficient, good physical-chemical stability at high temperature and high resistance to the oxidation, and the possibility of growing epitaxially on Si substrates. In addition to these material properties, it overcomes ecological and resources problems because of its nontoxicity and the rich deposits that are present on earth. So it is expected to be a useful promising material for solar cells with theoretical efficiencies from 16 to 23 % in the future. In addition, recently it was reported that amorphous forms of iron disilicide also indicated semiconducting properties. It is very attractive at both the physical and engineering points of view because it can be grown easily on various kinds of substrate at room temperature. In this study, we fabricated thin films both by pulsed laser deposition (PLD) and by facing target DC sputtering (FTDCS) which was advantageous for the engineering applications, for the purpose of applying for the electric device such as a solar sell..

Fabrication of semiconductor/ferromagnetic metal atrificial lattices and study on their new physical phenomena based on spin-dependent conductionkeyword : heterostructure, semiconductor, ferromagnetic, interlayer coupling, artificial lattices2001.04～2011.03【Research in a semiconductor / ferromagnetic metal superlattice】
There have been few studies for the hetero-structure, such as the ferromagnetic metal /semiconductor multi-layered film, because the fabrication is extremely difficult. However, this hetero-structure has a possibility that the anti-ferromagnetic and ferromagnetic coupling among the ferromagnetic layers can be switched through the intermediary of the semiconducting layers, whose electrical band structure can be changed by the heat and photons. Fe-Si system has both the semiconducting phases such as beta-FeSi2, amorphous FeSi2 and FeSi, and the ferromagnetic ones such as Fe3Si and Fe、and expected as a new candidate for spintronic. We fabricate the Fe3Si or Fe / nanocrystalline (NC) FeSi2 multi-layered films, and study a new physical properties at optical, electrical and magnetic points of view..

Fabrication of diamond-like carbon films by pulsed laser depositionkeyword : DLC, PLD1996.04～2003.03【Fabrication of hydrogen-free diamond-like carbon films by physical vapor depositions and their application for coating】
Diamond-like carbon (DLC) have been adapted for coating on a metal mold, a tool and a machine part, because it has a high hardness, a low friction coefficient, a high adhesion and so on. DLC containing hydrogen has been mainly fabricated by a chemical vapor deposition method and have been applied for various industries as mentioned above. Hydrogen-free DLC prepared by physical vapor deposition methods has received much attention in recent years, because the deposited films have more excellent properties than those prepared by CVD. In general, hydrogen-free DLC is prepared by sputtering now. In this study, in order to grow a hydrogen-free DLC film having more excellent properties, we adapt a pulsed laser deposition method using a graphite target..

Current and Past Project

Ultrananocrystalline diamond (UNCD)/hydrogenated amorphous carbon (a-C:H) composite (UNCD/a-C:H) films, which are comprised of diamond crystallites with diameter of less than 10 nm embedded in an a-C:H matrix, possess large optical absorption coefficients in the visible range due to a large number of grain boundaries. Here, the grain boundaries exactly means that the interfaces between UNCD crystallites and those between UNCD and an a-C:H matrix. We have confirmed evident photoconduction corresponding to the large optical absorption. In this work, we are committed to apply this photoconduction to photovoltaics.

Ali M. Ali, Mohamed Egiza, Koki Murasawa, Yasuo Fukui, Hidenobu Gonda, Masatoshi Sakurai, Tsuyoshi Yoshitake, Negative bias effects on deposition and mechanical properties of ultrananocrystalline diamond/amorphous carbon composite films deposited on cemented carbide substrates by coaxial arc plasma, Diamond and Related Materials, 10.1016/j.diamond.2019.04.031, 96, 67-73, 2019.06, Ultrananocrystalline diamond/amorphous carbon composite (UNCD/a-C) films were deposited on negatively biased cemented carbide (WC-Co) substrates by coaxial arc plasma deposition. The deposition rate is increased to be 0.9 nm/s, which is approximately 3 times larger than that of films deposited under no bias condition. In addition, the critical load in scratch tests was enhanced to be 31 N, which is 4 times more than that of the no bias films. On the other hand, the hardness was slightly degraded by employing the negative bias. From electrical diagnostics of the bias application, it was found that the negative bias is immediately compensated by the arrival of highly-dense positive carbon ions at the substrate and the substrate is weakly positively charged after the compensation. This might be the main reason for the degraded hardness by the bias application, Since the positive bias deaccelerate carbon ions, which facilities the formation of sp2 bonds..

3.

Eslam Abubakr, Abdelrahman Zkria, Yūki Katamune, Shinya Ohmagari, Kaname Imokawa, Hiroshi Ikenoue, Tsuyoshi Yoshitake, Formation of low resistivity layers on singlecrystalline diamond by excimer laser irradiation, Diamond and Related Materials, 10.1016/j.diamond.2019.04.013, 95, 166-173, 2019.05, A singlecrystalline diamond (100)(Ib) plate immersed in 2% boric acid was irradiated by 193-nm ArF excimer laser beams for the formation of conductive layers on the surface of an insulating diamond substrate. From current-voltage measurements of the irradiated areas, it was confirmed that semiconducting layers with high conductivities are formed on the diamond surface. It was possible to form ohmic contacts by directly touching tungsten probes with the layer surface. Since Raman spectra exhibited only peaks due to diamond and no peaks due to amorphous carbon, the drastically enhanced conductivity is not attributed to amorphous carbon formation but due to the incorporation of boron atoms into the diamond subsurface from the dopant acid. Secondary ion mass spectrometric depth profile showed the incorporation of boron atoms up to 40 nm depths from the surface. From cathodoluminescence measurements at low temperatures, it was difficult to detect clear peaks for the substitutional incorporation of boron atoms into diamond lattices, which could be attributed to the small thickness of the doped layer for detection. The proposed technique is a new potential method for shallow doping and formation of conductive layers on singlecrystalline diamond surfaces..

Abdelrahman Zkria, Mahmoud Shaban, Takanori Hanada, Nathaporn Promros, Tsuyoshi Yoshitake, Current transport mechanisms in n-type ultrananocrystalline diamond/p-type Si heterojunctions, Journal of Nanoscience and Nanotechnology, 10.1166/jnn.2016.13663, 16, 12, 12749-12753, 2016.12, Nitrogen-doped ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) films were deposited on p-type Si substrates by coaxial arc plasma deposition. The deposited films possessed n-type conduction, and evidently formed pn heterojunctions with p-type Si substrates. The heterojunction devices showed typical rectification properties similar to those observed for conventional abrupt pn heterojunctions. The conduction mechanisms that govern current transport in these devices were analyzed using dark current-voltage measurements in the temperature range from 300 K to 80 K. The results revealed that a trap-assisted multi-step tunneling process is a dominant mechanism at lower temperatures and low forward bias. At least two defect levels with activation energies of 42 and 24 meV appear to activate this process. At moderate forward bias, the current followed a power-law dependence, attributable to a space-charge-limited current. This junction behavior might be owing to a large number of grain boundaries in the UNCD/a-C:H film that provide active centers for carrier recombination-tunneling processes at the junction interface..

Hiroshi Naragino, Aki Tominaga, Kenji Hanada, Tsuyoshi Yoshitake, A synthesis method of ultrananocrystalline diamond in powder employing a coaxial arc plasma gun, Appl. Phys. Express, doi:10.7567/APEX.8.075101, Vol. 8, No. 7 (2015) 075101., 2015.07, A new method that enables us to synthesize ultrananocrystalline diamond (UNCD) in powder is proposed. Highly energetic carbon species ejectedfrom a graphite cathode of a coaxial arc plasma gun were provided on a quartz plate at a high density by repeated arc discharge in a compactvacuum chamber, and resultant films automatically peeled from the plate were aggregated and powdered. The grain size was easily controlledfrom 2.4 to 15.0nm by changing the arc discharge energy. It was experimentally demonstrated that the proposed method is a new and promisingmethod that enables us to synthesize UNCD in powder easily and controllably..

Yuki Katamune, Shinya Ohmagari, Sausan Al-Riyami, Seishi Takagi, Mahmoud Shaban, Tsuyoshi Yoshitake, Heterojunction Diodes Comprising p-Type Ultrananocrystalline Diamond Films Prepared by Coaxial Arc Plasma Deposition and n-Type Silicon Substrates , Jpn. J. Appl. Phys., 10.7567/JJAP.52.065801, Vol. 52, No. 6 (2013) 065801., 2013.06, [URL], Heterojunction diodes, which comprise boron-doped p-type ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) films prepared by coaxial arc plasma deposition and n-type Si substrates, were electrically studied. The current–voltage characteristics showed a typical rectification action. An ideality factor of 3.7 in the forward-current implies that carrier transport is accompanied by some processes such as tunneling in addition to the generation–recombination process. From the capacitance–voltage measurements, the built-in potential was estimated to be approximately 0.6 eV, which is in agreement with that in a band diagram prepared on the assumption that carriers are transported in an a-C:H matrix in UNCD/a-C:H. Photodetection for 254 nm monochromatic light, which is predominantly attributable to photocurrents generated in UNCD grains, was evidently confirmed in heterojunctions. Since dangling bonds are detectable by electron spin resonance spectroscopy, their control might be an important key for improving the rectifying action and photodetection performance. .

27.

Nathaporn Promros, Li Chen, Tsuyoshi Yoshitake, Evaluation of n-Type Nanocrystalline FeSi2/p-Type Si Heterojunctions Prepared by Pulsed Laser Deposition as Near-Infrared Photodetectors, J. Nanosci. Nanotechnol. , 10.1166/jnn.2013.7311, Vol. 13, No. 5 (2013) pp. 3577–3581., 2013.05, n-Type nanocrystalline (NC) FeSi2/p-type Si heterojunctions, which were prepared by pulsed laser deposition, were evaluated as a near infrared photodiode. The built-in potential was estimated to be approximately 1.1 eV from the capacitance–voltage measurement. These junctions showed a rectifying behavior accompanied by a large leakage current. The near infrared light detection performance was evaluated using a 1.33 m laser in the temperature range of 77–300 K. At a reverse bias of −5 V, the detectivity was 55×107 cm Hz1/2 W−1 at 300 K and it was dramatically enhanced to be 80×1010 cm Hz1/2 W−1 at 77 K. It was demonstrated that NC-FeSi2 is a new potential material applicable to NIR photodetectors operating at low temperatures..

E. Garratt, S. AlFaify, Tsuyoshi Yoshitake, Yuki Katamune, M. Bowden, M. Nandasiri, M. Ghantasala, D. C. Mancini, S. Thevuthasan, A. Kayani, Effect of chromium underlayer on the properties of nano-crystalline diamond films, Appl. Phys. Lett., http://dx.doi.org/10.1063/1.4774086, No. 102, Issue 1 (2012) 011913., 2013.01, [URL], This paper investigated the effect of chromium underlayer on the structure, microstructure, and composition of the nano-crystalline diamond films. Nano-crystalline diamond thin films were deposited at high temperature in microwave-induced plasma diluted with nitrogen, on single crystal silicon substrate with a thin film of chromium as an underlayer. Characterization of the film was implemented using non-Rutherford backscattering spectrometry, Raman spectroscopy, near-edge x-ray absorption fine structure, x-ray diffraction, and atomic force microscopy. Nanoindentation studies showed that the films deposited on chromium underlayer have higher hardness values compared to those deposited on silicon without an underlayer. Diamond and graphitic phases of the films evaluated by x-ray and optical spectroscopic analyses determined consistency between the sp2 and sp3 phases of carbon in chromium sample to that of diamond grown on silicon. Diffusion of chromium was observed using ion beam analysis which was correlated with the formation of chromium complexes by x-ray diffraction..

30.

Nathaporn Promros, Kyohei Yamashita, Ryuhei Iwasaki, Tsuyoshi Yoshitake, Effects of Hydrogen Passivation on Near-Infrared Photodetection of n-Type -FeSi2/p-Type Si Heterojunction Photodiodes, Jpn. J. Appl. Phys. , http://dx.doi.org/10.1143/JJAP.51.108006, Vol. 51, No. 10 (2012) 108006., 2012.10, Hydrogen passivation was applied to the initial epitaxial growth of n-type -FeSi2 thin films on p-type Si(111) substrates. Such passivation was applied at different gas inflow H2/Ar ratios ranging from 0 to 1.0. The photodetection performance of the photodiode fabricated at the optimum ratio of 0.2 was markedly improved as compared with those of the other samples. The quantum efficiency and detectivity were 2.08% and 5:40 109 cmHz1=2W1, respectively. The enhanced photodetective performance should be mainly because dangling bonds that act as trap centers for photocarriers are effectively inactivated by the passivation..

Shinya Ohmagari, Yūki Katamune, Hikaru Ichinose, and Tsuyoshi Yoshitake, "Enhanced growth of diamond grains in ultrananocrystalline diamond/hydrogenated amorphous carbon composite films by pulsed laser deposition with boron-blended graphite targets", Jpn. J. Appl. Phys., 10.1143/JJAP.50.035101, Vol. 51, No. 2 (2012) 025503., 2012.02, [URL], Heterojunction diodes comprised of p-type ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) and n-type Si, wherein 3 at. % boron-doped UNCD/a-C:H films were deposited on Si substrates by pulsed laser deposition, were electrically studied. The current–voltage (I–V) characteristics showed the typical rectification action with a leakage current density of 4.7 ×10-5 A/cm2 at a reverse voltage of -1 V. The carrier transport is expected to be in generation–recombination process accompanied by tunneling at low forward voltages of 0.1–0.5 V, and to be predominantly in tunneling at 0.5–1.0 V, from ideality factors estimated from the forward I–V curve. Grain boundaries in the UNCD/a-C:H film might act as centers for tunneling. From the capacitance–voltage measurement, the build-in potential of the heterojunction and an active carrier concentration in the p-type UNCD/a-C:H film were estimated to be 0.6 eV and 1.4 ×1017 cm-3, respectively. .

38.

Ken-ichiro Sakai, Takayuki Sonoda, Shin-ichi Hirakawa, Kaoru Takeda, and Tsuyoshi Yoshitake, Current-Induced Magnetization Switching in Fe3Si/FeSi2 Artificial Lattices, Jpn. J. Appl. Phys., 10.1143/JJAP.50.08JD06, Vol. 51, No. 2 (2012) 028004., 2012.02, [URL], Fe3Si/FeSi2/Fe3Si trilayered films were grown on Si(111) substrates at a substrate temperature of 300 °C by facing-targets direct-current sputtering, and current-induced magnetization switching in current-perpendicular-to-plane geometry was studied for the films wherein an antiferromagnetic interlayer coupling perpendicular to the plane was probably formed at room temperature. The appearance of a hysteresis loop in the electrical resistance–injection current curve well coincided with that of a hysteresis loop in the magnetization curve perpendicular to the plane. In addition, the hysteresis loop in the electrical resistance–injection current curve disappeared under large magnetic fields. The origin of the change in the electrical resistance for the injection current might be the change in the interlayer coupling. .

39.

Nathaporn Promros, Kyohei Yamashita, Chen Li, Kenji Kawai, Mahmoud Shaban, Toshihiro Okajima, and Tsuyoshi Yoshitake, n-Type Nanocrystalline FeSi2/intrinsic Si/p-Type Si Heterojunction Photodiodes fabricated by Facing-Targets Direct-Current Sputtering, Jpn. J. Appl. Phys., 10.1143/JJAP.51.021301, Vol. 51, No. 2 (2012) 021301., 2012.01, [URL], n-Type nanocrystalline (NC) FeSi2/intrinsic (i) Si/p-type Si heterojunctions, which were prepared by facing-target direct current sputtering, were evaluated as near-infrared photodiodes, and the effects of thin i-Si layer insertion on diode performance were studied. Their junction capacitance and reverse leakage current were clearly reduced compared with those of n-type NC-FeSi2/p-type Si heterojunctions. The capacitance–voltage curve implied that the effects of interface states is relatively suppressed by i-Si insertion. The near-infrared light detection performance was investigated using a 1.33 µm laser in the temperature range of 77–300 K. The detectivities at 300 and 77 K were 1.9 ×108 and 3.0 ×1011 cm Hz1/2 W-1, respectively, at a negative bias of -5 V, which were markedly improved compared with that of p–n heterojunctions. This might be because the formation of interface states that act as trap centers for photocarriers is suppressed. .

40.

Shin-ichi Hirakawa, Takayuki Sonoda, Ken-ichiro Sakai, Kaoru Takeda1, and Tsuyoshi Yoshitake, Temperature-Dependent Current-Induced Magnetization Switching in Fe3Si/FeSi2/Fe3Si trilayered films, Jpn. J. Appl. Phys., 10.1143/JJAP.50.08JD06, Vol. 50, No. 8 (2011) 08JD06., 2011.08, [URL], Fe3Si/FeSi2/Fe3Si trilayered films were grown on Si(111) substrates at a substrate temperature of 300 °C by facing-targets direct-current sputtering, and current-induced magnetization switching in current-perpendicular-to-plane geometry was studied for the films wherein an antiferromagnetic interlayer coupling perpendicular to the plane was probably formed at room temperature. The appearance of a hysteresis loop in the electrical resistance–injection current curve well coincided with that of a hysteresis loop in the magnetization curve perpendicular to the plane. In addition, the hysteresis loop in the electrical resistance–injection current curve disappeared under large magnetic fields. The origin of the change in the electrical resistance for the injection current might be the change in the interlayer coupling. .

Kenji Hanada, Tomohiro Yoshida, You Nakagawa, and Tsuyoshi Yoshitake, Formation of Ultrananocrystalline Diamond/Amorphous Carbon Composite Films in Vacuum by Using A Coaxial Arc Plasma Gun, Jpn. J. Appl. Phys., 10.1143/JJAP.49.125503, Vol. 49, No. 12 (2010) 125503., 2010.12, [URL], Ultrananocrystalline diamond (UNCD)/nonhydrogenated amorphous carbon (a-C) composite films were grown in vacuum using a coaxial arc plasma gun. From the X-ray diffraction measurement, the UNCD crystallite size was estimated to be 1.6 nm. This size is dramatically reduced from that (2.3 nm) of UNCD/hydrogenated amorphous carbon (a-C:H) composite films grown in a hydrogen atmosphere. The sp3/(sp3 + sp2) value, which was estimated from the X-ray photoemission spectrum, was also reduced to be 41%. A reason for it might be the reduction in the UNCD crystallite size. From the near-edge X-ray absorption fine-structure (NEXAFS) spectrum, it was found that the π*C=C and π*C≡C bonds are preferentially formed instead of the σ*C–H bonds in the UNCD/a-C:H films. Since the extremely small UNCD crystallites (1.6 nm) correspond to the nuclei of diamond, we consider that UNCD crystallite formation should be due predominantly to nucleation. The supersaturated condition required for nucleation is expected to be realized in the deposition using the coaxial arc plasma gun. .

Tsuyoshi Yoshitake, Present state of research on photodiodes comprising iron disilicides and problems awaiting solution, International conference and summer school on advanced silicide technology 2014, 2014.07, Semiconducting iron disilicide is a new candidate applicable to near-infrared-wavelength photoelec-tronic devices [1-3], because it possesses features such as a direct optical band gap of 0.85 eV above an indirect gap (0.76 eV) and a large absorption coefficient, which is 10^5 cm1 at 1.0 eV[4]. Since beta-FeSi2 can be epitaxially grown on Si due to small lattice mismatches, a heterojunction diode comprising a beta-FeSi2 thin film and singlecrystalline Si substrate is a device that can be briefly formed by employing vapor deposition. For near-infrared light detection in the Si/beta-FeSi2 heterojunction diodes, near-infrared light transmitted through the front-side Si substrate can be absorbed in the depletion region of the back-side beta-FeSi2 thin film. In our previous works, we have progresses researches on p-type Si/n-type beta-FeSi2 heterojunction diodes, totally from the epitaxially growth of beta-FeSi2 thin film on Si(111) by sputtering [5] to the evaluation of p-type Si/n-type beta-FeSi2 heterojunctions as photodetectors [6,7]. It was confirmed that beta-FeSi2 in the heterojunction evidently con-tributes to the photodetection of near-infrared light from the photoresponse spectrum of the heterojunction, as shown in Fig. 1. In addition, as shown in Fig.2, the heterojunction clearly exhibited current due to photogenerated carriers for 1.33 micrometer monochromatic light in the I-V curves in comparison with that in the dark. The detectivity at temperatures lower than 100 K reach approximately 2*10^11 cmHz^1/2 /W, which is comparable with that of existing near infrared photodiodes comprising PbS and InAs at the same temperature. However, the external quantum efficiency is less than 10 % [6,7]. In this presentation, the progress thus far of our research and recent problems that we are facing and should be solved for the next step will be introduced. A serious problem for p-type Si/n-type beta-FeSi2 heterojunctions is that a barrier due to a band offset appears in the valence band and it prevents from the flow of photogenerated carriers from the n-type beta-FeSi2 layer to the p-type Si layer. The opposite combination, namely n-type Si/p-type beta-FeSi2, is structurally ideal because of it has no barriers due to the band offset. In order to form p-type -FeSi2, the residual carrier density should be reduced for controlling the conduction type. Carbon doping, which might be effective for a reduction in the carrier density, will be introduced.

【Graduate School】The affiliation for graduate school education is Quantum Materials Physics Laboratory, Department of Applied Science for Electronics and Materials. I give two lectures every year as follows. Advanced Topics of Quantum Materials Physics Elemental Quantum PhysicsIn addition, I conrtibute to a lecture shared by deparment professors

【Undergraduate School】I have two classes on elemental mechanics. In addiiton, I join two shared lectures on renewable energy.

Member of the executive committee, The 1st Symposium on Kankyo-Semiconductors (1999).

Member of the executive committee, Symposium on Optics (1996).

【The others】Lecturer, the training institute organized by The Japan Cooperation agency (JICA) and Kyushu University (the year 2006).

Lecturer, the training institute organized by The Japan Cooperation agency (JICA) and Kyushu University (the year 2005).

Lecturer, the training institute organized by The Japan Cooperation agency (JICA) and Kyushu University (the year 2004).

Lecturer, the training institute organized by The Japan Cooperation agency (JICA) and Kyushu University (the year 2003).Technical advisor, Kyushu TLO Company, Limited (the year 2000-2003)Lecturer, the university xtension(the 2003)